Efficacy and feasibility of out-of-plane patient shielding during CT scanning

Transcription

1 Efficacy and feasibility of out-of-plane patient shielding during CT scanning Poster No.: C-1570 Congress: ECR 2013 Type: Authors: Keywords: DOI: Scientific Exhibit B. Klasic, Z. Brni#, Ž. Kneževi#, J. Plascak, V. Vidjak; Zagreb/HR Radioprotection / Radiation dose, CT, Radiation safety, Dosimetric comparison /ecr2013/C-1570 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 17

2 Purpose Computed tomography (CT) is a sectional imaging technique that uses a collimated x-ray beam perpendicular to the body axis to acquire image of a body slice of desired width. CT is playing an increasingly important role in the diagnosis of a wide variety of disorders. As a digital modality, CT can provide an excellent display of anatomic structures and pathology, often leading radiologists and clinicians from other specialities in a position to forget the high price of increased radiation load. Expanding use of this diagnostic modality resulted in making it the major source of radiation exposure to population from diagnostic x-rays. In countries with developed healthcare it contributes up to 47% of annual collective dose from medical radiation exposures [1]. Exposure to ionizing radiation is of concern because evidence has linked exposure to lowlevel ionizing radiation at doses used in medical imaging to the development of cancer. Multiple CT scans over time can deliver radiation exposure equivalent to that received by long-term survivors of the Hiroshima and Nagasaki atomic bombs (2). With every source of medical radiation exposure it is necessary to permanently establish the balance between benefits and risks. Many international organizations have published the guidelines that should help the standardization of CT examinations and optimization of radiation doses on patients (3). Since its introduction, it has been known that CT is related to high radiation dose to the patient. Due to the fact that CT is classified as high radiation dose procedure (4), it is essential to comply with the principles of ALARA (keeping radiatio doses As Low As Reasonably Achiavable). One of major ways to reduce radiation exposure to workers or to population is shielding. We chose to investigate the covering of tissues outside of the field of CT scanning because it does not affect image quality and is easy to use in daily practice. The purpose of our study was to evaluate effectiveness of out-of-plane lead shielding during CT scanning as a mean of patient scatter radiation protection and to demonstrate feasibility of this procedure in clinical settings. Methods and Materials Population and sample: Page 2 of 17

3 Our study included 220 randomly selected patients (117 men and 113 women) undergoing routine CT scanning as a part of their clinical treatment over five-month period. Scanning equipment was Shimadzu SCT-7800TX (Shimadzu, Japan), the most common model of CT scanners in Croatia. Measurements were performed for most common regions of interest: head, thorax and abdomen. For each region standard scanning parameters were used for all patients. Anthropometric parameters recorded for each patient were gender, age, height and weight. Body mass index (BMI) was calculated. Shielding and measurement: The doses on patients were measured with tissue equivalent thermoluminescent dosimeters (TLD) based on well known LiF:Mg, Ti detectors (TLD-700). The dosimeters were packed in dark polyethylene foil and in rubber holders and placed on the body of the patient on the positions of the radiosensitive organs and always outside the scanning field (Fig. 1). For CT of the head positions of dosimeters were: over thyroid gland, breast and gonads; for thoracic scans: thyroid and gonads; and for abdominal scans: thyroid, breast and testes only. First dosimeter was placed directly on the skin, and then the body was covered with a standard single front lead apron with 0.5 mm lead equivalent. The thyroid gland was shielded by protective collar. (Fig. 2-4). Second dosimeter was placed above the first over lead protection. Phantom dose measurements were performed with an Alderson RANDO phantom with same distribution of TLDs as in patients. The total number of measured patient doses was 940 and phantom doses 155. Statistical analysis: Analysis of the statistics group and interpretation included only measurements that obeyed the normal distribution. Outlying elements were omitted. We explored the relationship between various variables with multivariate statistical analysis. Images for this section: Page 3 of 17

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5 Fig. 1: Measurement points for TLDs Fig. 2: Neck shielding with protective collar Page 5 of 17

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7 Fig. 3: Breast shielding with lead apron Page 7 of 17

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9 Fig. 4: Pelvic shielding with protective lead apron Page 9 of 17

10 Results Our research has shown that the lead shielding is simple to manoeuvre. It was easy for radiographers to move and handle lead apron and position it properly on patients body. Simple procedure of shielding made our patients feel more confident, without causing any discomfort or arousing fear from radiation. After they were explained the benefit and complete safety, only very small number of patients refused to use shielding before the scanning. The average time needed to set up an apron was less than a minute (55 seconds), and twice as long for obese patients (BMI over 30). The lead shielding is more difficult for larger patients with higher BMI. For those patients trying to get the lead apron not to slide from the patient prooved to be difficult. For very obese patients it is difficult to eliminate the uncovered gap at the sides of the apron and usually impossible to get the shielding all the way around. Scatter doses measured at skin under lead apron and over it are shown in Table 1. Values are divided by scanning volumes and regions of interest. TLD position REGION of interest Thyroid Breast Gonads Above (mgy) Scanning volume (CT of) HEAD THORAX ABDOMEN 0,45 ± 0,21 0,35 ± 0,24 0,16 ± 0,10 Below (mgy) 0,81 ± 0,31 0,71 ± 0,38 0,27 ± 0,19 In (mgy) Above (mgy) total 1,26 ± 0,46 1,06 ± 0,39 0,43 ± 0,22 0,20 ± 0,13-0,29 ± 0,18 Below (mgy) 0,19 ± 0,11-0,86 ± 0,43 In (mgy) Above (mgy) total 0,39 ± 0,19-1,15 ± 0,51 0,08 ± 0,04 0,14 ± 0,11 0,38 ± 0,23 Below (mgy) 0,08 ± 0,05 0,21 ± 0,15 0,66 ± 0,55 In (mgy) total 0,16 ± 0,07 0,35 ± 0,09 1,04 ± 0,70 Page 10 of 17

11 Above = position over lead apron Below = position under lead apron In total = sum of measured does over and under lead apron Value and percentage of scatter dose reduction is shown on charts (Fig. 5-7 ), also divided by scanning volumes and regions of interest. Phantom measurements showed a similar unshielded surface doses, but a larger reduction when shielding was added (at least 55% for thyroid, 67% for breast and 63% for gonads). In our study for organs further away from the scanning zone (eg gonads for CT of the thorax), the largest contribution to the total dose of scatter radiation derived from the internal scattering within patient's body. For organs close to the scanning zone (eg thyroid for head CT), contribution to the total dose from external and internal scattering was equal. Statistical analysis showed medium-strong negative correlation between BMI and dose reduction (r = -0,55) and strong correlation with under-the-cover dose and reduction (r=0,85). Images for this section: Page 11 of 17

12 Fig. 5: Scatter radiation dose reduction for CT of head for specific regions of interest. Page 12 of 17

13 Fig. 6: Scatter radiation dose reduction for CT of thorax for specific regions of interest. Page 13 of 17

14 Fig. 7: Scatter radiation dose reduction for CT of abdomen for specific regions of interest. Page 14 of 17

15 Conclusion The efficacy of lead cover shielding for reduction of scatter to various superficial organs was already confirmed for many imaging procedures (5,6,7,8,9,10). Our measurement results show quite a wide range of values. This should primarily be attributed to the fact that our research was conducted in vivo, where the anatomical differences between individual patients can significantly affect the measured dose. In our research, we ensured that dosimeters were laid precisely over the specific radiosensitive tissues, such as distributed on the body of each individual patient (like Brnic et al.) and not always on same predetermined position (like Beaconsfield et al.). We believe that our method of measurement is more suitable to the actual situation in daily clinical practice. In contrast, measurements on phantoms are much more uniform because dosimetry is done always in the same position on the phantom, which always has standard physical characteristics. Our measured scatter doses were higher in comparison to most authors (5,8,9). The percentage of scatter dose reduction in our study was lower than in most of the older researches (7,8,9). This is partly because their measurements were performed mostly on phantoms. The difference was also due to non-standardized ways of shielding and dosimeter placement. Some recent phantom studies (11) have shown scatter radiation dose reduction comparable to our values. In our opinion this is due to the fact that they are mainly concentrated on the relationship between the dose reduction and the distance from the scanning area. In our study, the percentage of dose reduction also correlates with distance from the scanning area. Although the level of exposure reduction is relatively low when compared to total dose of CT examination, the procedure might have significant transcend effects. It is out of discussion that exposure reduction, although low, undoubtedly fit to ALARA concept, and lead to reduction of stochastic risks, however small this reduction to be. This reduction is even more desirable in younger patients, especially those who undergo repeated CTs in the course of their treatment (e.g. malignant hematological disorders), and the cumulative breast and thyroid dose can significantly raise the risk of malignancy of these organs (12). As many of those patients with a good survival prognosis are fertile, the protection of their gonads should be an imperative, keeping in mind possible latency of gene mutations and appearance of its effects in offsprings after generations. Simple protection measures, as the one described, help to build an atmosphere of radiation protection discipline, which is easy to lose if not permanently corroborated Page 15 of 17

16 by emphasizing its efficacy, simplicity and necessity. Traditionally, in many counties technologist have a limited awareness on protection of patients, many of them being unconscious about the doses delivered to patients in routine CT scanning. Everyday practice of patients covering, might serve as a "reminder" on the dose problem, forcing them to be alert of other protection principles (justification, optimization). It is well documented, that simple procedures of a special care of the patient could have positive psychological impact in staff-to-patient transfer, reducing anxiety (13). Patient satisfaction with imaging procedures is closely correlated to the feeling of safety, therefore, the act of covering may help built an atmosphere of confidence among patients and staff, thus alleviating the cooperation and compensating possible shortages which can emerge in everyday patient care. Contraindications for patient shielding against scatter are rare, if any of them can be considered absolute. The feasibility of this procedure is compromised in urgent procedures, uncooperable or agitated patients, children, patient with bandages, tubings and catheters. In rare situations the apron may collide with patient table translation through gantry, or disturb/hinder the manipulation of patient in emergent situations (the need for resuscitation etc.). The procedure is also not recommended in patients with high risk factors for severe contrast adverse effects, as the masking of patient skin prevents early recognition of possible urticaria which can be a sign of more severe threatening adverse reaction. As the procedure of out-of-plane body shielding is simple and low-cost it is reasonable to promote this measure widely in clinical practice. Like a smile that costs nothing, is available anywhere and gives a lot - patient shielding may have a similar power. References 1. HartD,WallBF. UK population dose from medical X-ray examinations.eur J Radiol 2004;50: Smith-Bindman R, Lipson J, Marcus R, et al. Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Arch Intern Med. 2009;169(22): European Community. European guidelines on quality criteria for computed tomography. Report EUR Brussels, Belgium: European Community, European Community. Council Directive 97/43/EURATOM, 30 June 1997, on health protection of individuals against the dangers of ionizing radiation in relation to Page 16 of 17

17 medical exposure (repealing Directive 84/466/Euratom). Off J Eur Commun 1997; L180, 40: Brni# Z, Veki# B, Hebrang A,Ani# P. Efficacy of breast shieding during CT of the head. Eur Radiol Nov, 13(11): Hohl C, Mahnken AH, Klotz E, Stargardt A, Muhlenbruch G, Schmidt T, Gunther RW, Wildberger JE. Radiation dose reduction to the male gonads during MDCT: the effectiveness of a lead shield. Ajr 2005;184: Price R, Halson P, Samson M. Dose reduction during CT scanning in an anthropomorphic phantom by the use of a male gonad shield. The British jurnal of radiology. 1999:72: Hidajat N, Schroder RJ, Vogel T, schedel H, Felix R. The efficacy of lead shielding in patient dosage reductionin computed tomography. Rofo. 1996;165: Beaconsfeld T, Nicholson R, Thornton A, Al-Kutoubi A (1998) Would thyroid and breast shielding be beneficialin CT of the head? Eur radiol Iball G, Kennedy E, Brettle D, Modelling the effect of lead and other materials for shielding of the foetus in CT pulmonary angiography. Br J Radiol, 2008; 81: Iball GR, Brettle DS, Organ and effective dose reduction in adult chest CT using abdominal lead shielding. Br J Radiol Nov;84(1007): Kleinerman RA. Cancer risks following diagnostic and therapeutic radiation exposure in children. Pediatr Radiol. 2006;36(Suppl 2): Radiation Protection, Brusin JH, Radtech May/June 2007 vol. 78 no Personal Information Page 17 of 17